The easiest way I have found to do this is to set up a Multisite installation with subdomain installs, and run the plugin “WP Ultimo” to manage signups. It does exactly what you’re looking for: duplicates a template site on demand, and activates various plugins depending on which plan the customer has signed up for. You can offer a 30 day trial subscription for free, you can offer coupons, and Arindo has more recently integrated support for OpenSRS if you want to sell domains through your site. I am not affiliated with them, but I use their product and based on my experience I would recommend it to you. Best of luck!
Reference: https://wpultimo.com/